Flexible composite couplings for transmission of torque between driving and driven members have been under development for a number of years. Specifically, work has been done in the areas of increasing torque carrying capacity, increasing misalignment capability, better balancing and increasing service life of the couplings. In general, flexible composite couplings are manufactured from filamentary reinforcing material with a matrix or binder material impregnating the fibers to add form. These couplings are lightweight and very well suited for high speed applications because they require only minimal balancing. These couplings connect a driving member to a driven member and allow transmission of torque, yet simultaneously therewith, they accommodate axial misalignment and cocking misalignment of the driving member relative to the driven member.
The Morrill patent (U.S. Pat. No. 2,195,993) discloses a flexible coupling with a flexible member 15 of elastomer or fabric reinforced elastomer construction connecting to the annular flanges 13 at the outermost point thereby reducing stress on the flexible member. The Ernst et al. patent (U.S. Pat. No. 3,977,273) discloses a flywheel for an inertial guidance system comprised of one or more wound filaments such as carbon or boron with a binder such as a resin. The Weible patent (U.S. Pat. No. 4,116,018) discloses a wound composite universal joint comprising wound elongate elements or fibers preferably coated with a binder resin and at least two large diameter portions and at least one small diameter portion. Application of torque places certain load-carrying filaments substantially in tension. Shown in FIG. 1, is the connection of the flexible portion to the disks at the outermost portion, as well as a removable central universal joint. Although the Weible coupling has the benefits of being light weight and having substantial torque carrying capacity, it has cocking and axial stiffnesses that are higher than desirable. This is because it is necessary to space the large diameter portions 28 and 30 apart by a substantial distance in order to wind the coupling and this spacing results in a high axial compression component of the flexing element while undergoing cocking misalignment.
The commonly assigned Hannibal patent (U.S. Pat. No. 4,391,594) discloses a flexible coupling for transmitting torque and accommodating cocking and axial alignment. The coupling is comprised of a pair of hubs 13 and 14 and a reinforcing ring 23. A reinforcing fiber strand is wrapped from one hub 13, across the reinforcing ring 23, and to the other hub 14. The strand is impregnated with resin and wound in a geodesic path. A second commonly assigned Hannibal patent (U.S. Pat. No. 4,569,667) discloses a flexible coupling for transmitting torque and accommodating misalignment. The coupling is comprised of a pair of plates 57 and 59 with protruding pins 63 and a reinforcing ring 23. A reinforcing fiber strand is wrapped from the pins 63 on one plate 57, across the reinforcing ring 23, and to the other pins 63 on the other plate 59. The strand is resin impregnated and wound in a geodesic path. Although both these couplings exhibit soft cocking and axial stiffness and high torsional stiffness, they tend to lack the strength of the Weible '018 concept, wherein the bonds are at the maximum diameter of the coupling. Most notably, all these couplings of the Hannibal '667 and '594 and the Weible '018 all lose their initial pretension in the fibers, thus limiting the torque carrying capacity.
The Bongers et al. patent (U.S. Pat. No. 4,577,736) describes a tubular member for transmitting torque between axially spaced members. The member includes wound fiber roving material and a binding resin matrix material. A winding angle of +/-45 degrees is desirable for torsional rigidity and low bending stiffness. Matuska et al. (U.S. Pat. No. 4,666,753) discloses a composite coupling for transmitting torque between axially spaced members. The coupling includes layers of fiber material such as Kevlar.RTM. fiber and a thermosetting or thermoplastic resin matrix material such as American Cyanamid epoxy 1806. A fiber roving or tape is wound about the rim of the coupling in a circumferential manner for reinforcement in order to prevent oil-canning of the part as it is exposed to high temperatures.
The commonly assigned, Gupta patent (U.S. Pat. No. 4,863,416) discloses a composite shaft for transmitting torque between axially spaced couplings. The member includes layers of overlapped anisotropic layers each comprised of parallel filaments. Described is the winding angle of 55-65 degrees for resulting in a desirable torsional to bending stiffness ratio while reducing bending stress in the composite shaft. The commonly assigned McGuire patent (U.S. Pat. No. 4,968,286) discloses a filament wound coupling which is geodesically wrapped over a removable mandrel. The coupling 10 includes a pair of hubs 12 and 14 with a plurality of projecting pins 26, 28. The filaments 38 are wrapped in a geodesic pattern from one hub 12, over the reinforcing ring 34 and onto the other hub 14. The filaments are secured to the pins, and the pins have a threaded portion for easily accepting the driving and driven members.
All of the above couplings exhibit good performance for their intended purpose. However, it should be understood that the prior art couplings which exhibit both low axial and cocking stiffness have low torsional strength and fatigue life and, conversely, the prior art couplings which exhibit high torsional strength and fatigue life have axial and cocking stiffnesses which are too high. In addition, all prior art composite couplings tend to lose their initial fiber pretension, either during manufacture or shortly thereafter, thus limiting their torque capacity.